The Air Force Research Laboratory (AFRL) utilizes a multi-step process to make rocket fuel. In the process, the precursor 2-Hydroxyethylhydrazine (HEH) is pumped into a reactor under a nitrogen purge, set at 0.5° C. The HEH is agitated while deionized water is slowly added to the reactor. The mixture is agitated for 10 minutes to reach a consistent temperature of about 1° C. The mixture is continuously agitated while nitric acid (HNO3) is slowly added. The pH of the mixture is constantly measured throughout the process. The temperature of the mixture is monitored in order to prevent it from increasing above 10° C. The pH range starts at about 8-9 at the beginning of the nitric acid addition, and decreases to about 6-7 near the end of the addition. The addition of nitric acid is slowed, and the reaction is sampled. Enough acid is added to keep the pH in the range of 4.8-5.0. When the HEHN is the correct pH range, the liquid product (light yellow color) is drained out of the bottom of the reactor and into a pre-cleaned container.
The newly synthesized HEHN is transferred into a rotary evaporator where the water is removed and neutralized. This process continues until the overall water percentage of the HEHN reaches 10 percent. Smaller samples can be put back into the rotary evaporator to lower the water content to 3 percent at a later time. The HEHN is sparged with nitrogen to remove remaining water, then removed from the rotary evaporator and put into a storage vessel under nitrogen. A sample of the final product is used for testing. The pH and percentage HEHN and water are checked by potentiometric titration. The target pH is in the range of 4.8-5.0, producing a mixture of about 95 weight percent HEHN with water. The HEHN is kept packaged under N2. The filled vessel is removed and placed in a proper storage location for a D.O.T. 1.3 explosive material.
The multi-step process used by AFRL requires dilution with water to control the nitration rate of HEH to HEHN. The AFRL process is time consuming, requiring multiple steps to achieve a uniform mixture of HEHN with the desired volume percent water. To produce a hypergolic green fuel (HGF), HEHN produced by the AFRL method described above must be mixed with the solvent Acetone, adding an addition process step.